1. Field of the Invention
The present invention relates generally to fuel injection assemblies for gas turbine engines, and more particularly, but not by way of limitation, to relatively small-size, high-performance fuel injectors of a type useful for rotary wing aircraft. The invention is also useful in applications where a lean direct injector is desired to reduce nitrous oxide (NOx) emissions.
2. Description of the Prior Art
There is an ongoing need in the art of advanced gas turbine combustors for fuel nozzles that can provide good atomization and fuel-air mixing; a high fuel-to-air turndown ratio; and good high temperature performance, such as to provide resistance to fuel coking.
A high temperature fuel nozzle design program was funded by the Naval Air Propulsion Center about 1990. Two papers discussing technologies for thermal insulation of fuel passages for different types of nozzles were published. The first is ASME 92-GT-132, xe2x80x9cInnovative High Temperature Aircraft Engine Fuel Nozzle Designxe2x80x9d by Stickles, et al. (1992). The second is xe2x80x9cDevelopment of an Innovative High-Temperature Gas Turbine Fuel Nozzlexe2x80x9d, by Meyers, et al, J. of Engr. for Gas Turbines and Power, Vol. 114, p. 401 (1992).
Another line of development work in the field of high performance fuel injectors for gas turbine engines is that group of designs referred to as lean direct injection (LDI) designs. Lean direct injection designs seek to rapidly mix the fuel and air to a lean stoichiometry after injection into the combustor. If the mixing occurs very rapidly, the opportunity for near stoichiometric burning is limited, resulting in low NOx production.
Also, the prior art has included injectors using fuel momentum to direct fuel across an air stream. U.S. Pat. No. 4,854,127 to Vinson et al. discloses at FIGS. 6-8 thereof a momentum staged injector wherein at high power operation the momentum of a fuel jet carries the fuel across a central air stream to reach an outer fuel filmer lip.
There is a continuing need for improvement in the design of high performance fuel injectors for gas turbines. In some instances the primary focus is upon stable low power performance. In others relative size and power output are critical. In still others low NOx emissions are critical.
The present invention provides improvements upon the injector design having a bifurcated recirculation zone as disclosed in the referenced Crocker et al. application, and particularly the present invention provides a design that is especially useful for relatively small-sized, high-performance combustors. The present design enables stable combustion at low power and provides good fuel-air distribution and mixing at high power. The high-power mixing results in low pattern factor and/or low NOx emissions. Furthermore, the design is capable of achieving the required low-power and high-power performance with a single fuel circuit.
In a first embodiment, a fuel injector apparatus includes a tip body having an aft facing tapered surface, the tip body having a fuel passage defined therein, and having at least one fuel injection port communicating the fuel passage with an exterior of the tip body. The apparatus further includes a central air supply conduit having a radially inward tapered aft portion disposed concentrically about and spaced radially from the aft facing tapered surface of the tip body to define an air sweep passage oriented to direct a central air stream aft and radially inward. A main fuel filmer lip is located concentrically about the tip body and in a path from the fuel injection ports. In a low pressure operating mode, fuel is entrained in the central air stream from the atomizer tip. In a high-power operating mode, fuel penetrates the central air stream and impinges upon the fuel filmer lip where it is air blast atomized by the main air stream flowing past the fuel filmer lip.
In another embodiment a fuel injection apparatus includes a fuel injector, one and only one fuel supply circuit communicated with the fuel injector, and the fuel injector has air supply conduits defining a central air stream, a main air stream and a bifurcated recirculation zone separating the central air stream from the main air stream. The central air stream is axial so that there is no axial recirculation on the centerline. At least one fuel injection port is communicated with the fuel supply circuit and oriented such that at fuel supply pressures within a low power operating range a majority of fuel is entrained in the central air stream, and at fuel supply pressures within a high pressure operating range a majority of injected fuel is entrained in the main air stream.
In another embodiment, methods of injecting fuel into a combustor are provided. The methods include:
(a) providing a fuel injector;
(b) flowing a central air stream over the fuel injector, the central air stream becoming axial downstream of the fuel injector and having no axial recirculation zone;
(c) flowing a main air stream concentrically outside of the central air stream;
(d) creating a bifurcated recirculation zone separating the central air stream from the main air stream; and
(e) providing fuel to the fuel injector, during both a low power operating mode and a high power operating mode, through a single fuel supply path, fuel being supplied during the lower power operating mode at a pressure with a first pressure range such that a majority of the fuel is entrained in the central air stream, and fuel being supplied during the high power operating mode at a pressure within a second pressure range, higher than the first pressure range, such that a majority of the fuel penetrates the central air stream and is entrained in the main air stream.
It is therefore an object of the present invention to provide improved high performance fuel injection apparatus for gas turbine combustors.
Another object of the present invention is the provision of a fuel injection apparatus which enables stable combustion at low power and good fuel-air distribution and mixing at high power.
Another object of the present invention is the provision of relatively small, high-performance fuel injectors.
And another object of the present invention is the provision of simple fuel injectors which are economical to manufacture.
Still another object of the present invention is the provision of fuel injectors that result in low pattern factor.
And another object of the present invention is the provision of fuel injectors which provide for low NOx emissions.
Still another object of the present invention is the provision of fuel injectors which provide good atomization and fuel-air mixing.
And another object of the present invention is the provision of fuel injectors having a high fuel-to-air turndown ratio.
Still another object of the present invention is the provision of fuel injector apparatus having good high temperature performance as evidenced by resistance to fuel coking in the fuel passages and fuel injection ports.
Other and further objects features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.